1. Technical Field of the Invention
The present invention relates to cellular telephone networks and, in particular, to the monitoring of cellular telephone calls by law enforcement agencies.
2. Description of Related Art
When law enforcement agencies are authorized to monitor telephone calls to obtain evidence for use in criminal investigations, perhaps the most important piece of information they obtain other than the recorded voice conversation itself is the identification of the parties participating in the call. In a conventional wireline telephone network, this information is readily accessible because a physical connection exists between the A-party (calling party) and the B-party (called party) to the call allowing the call to be traced, and because the communications protocols within the network support the transmission of party identification information like telephone numbers. Because of the lack of a physical connection and the limitations present in some communications protocols and switch operations, such party identification information is not so readily available during law enforcement agency monitoring of a cellular telephone call. The party identification problem is most prevalent with respect to being able to determine the identity of the A-party to the call.
The signaling protocols used between some telecommunications exchanges provide for the transmission of only two numbers in connection with the set-up of a cellular call. The first number comprises the actual telephone number of the B-party. The second number comprises a roamer number used to route the call within the cellular network. With space provided for only two numbers, there is no room within those signaling protocols for conveying the telephone number of the A-party to the cellular call. If the B-party is the party to be monitored, A-party information is then not typically made available to the monitoring law enforcement agency at the point where the telephone tap is made.
There is a need then during law enforcement agency monitoring of a cellular call for complete party identification information to be provided. In particular, there is a need to obtain information on the A-party to the monitored cellular call.